1. Field of the Invention
The present invention relates to television systems and more specifically to a method and apparatus for processing multiple streams of data encoded in respective vertical blanking interval (VBI) channels.
2. Related Art
Data is often encoded along with images and voice in television signals. Typically, a channel (xe2x80x9ctelevision signal channelxe2x80x9d) of a television signal contains a program component (which specifies the displayed images and accompanying audio component) and synchronization signals. The synchronization signals specify the transitions to next horizontal lines within an image frame, and between image frames. The portion of television signal received corresponding to transition between image frames is commonly referred to as vertical blanking interval (VBI).
Data is often encoded in VBI channels. Examples of such data include teletext data and extended data services (XDS) related data. Typically, a broadcaster includes the data in VBI portion and a user system (e.g., a set-top operating in conjunction with a television system, or a chip-set implemented within a television system) may need to recover the data.
A user system may further need to recover the data encoded in multiple VBI channels, with each VBI channel being related to a television signal channel. Such a need may exist, for example, when a user system needs to display closed captioning data received on one channel while recovering television guide type data received on another channel in parallel.
Recovery of data in each VBI channel often requires the implementation of an equalizer to perform a task commonly referred to as deghosting. Deghosting in turn refers to eliminating any faint second images which may be otherwise present in television displays due to noise components resulting from phenomenon such as echo. Deghosting is often implemented using integrated circuits executing software/firmware instructions.
In a prior embodiment, an equalizer may be implemented associated with VBI channel. Unfortunately, such a solution may require a large number of gates (components), which consume an unacceptable amount of space and electrical power. Accordingly, what is needed is a method and apparatus which enables data in multiple streams of a VBI channels to be recovered without requiring an excessive number of gates.
The present invention minimizes the number of gates required for recovering data elements from multiple VBI channels by sharing an equalizer among the multiple television signal channels. An ADC and a clock and data recovery circuit may be associated with each channel. The ADC over samples at least the VBI portion of the channel.
The clock and data recovery circuit examines the over sampled samples to recover the encoding clock used to encode the data, and selects a subset of the over sampled samples according to the recovered clock. A memory potentially shared by all the channels, may store the subset of the samples related to all the channels.
An equalizer then processes the subsets of samples to perform tasks such as deghosting, and the data elements in the VBI channels may be recovered as a result. In one embodiment, the equalizer is implemented as a fractional equalizer well known in the relevant arts.
An embodiment of the above described recovery circuit is implemented within a television system. Another embodiment may be implemented within a set-top box. However, it should be appreciated that the present invention may be implemented in, among others, any devices which process VBI channels.
Thus, an aspect of the present invention enables the number of gates in a data recovery circuit to be minimized as an equalizer may be shared among several paths, with each path generating digital data elements potentially with ghosting effects.
An aspect of the present invention enables the space and energy consumption to be minimized as the number of gates required to implement data recovery circuit may be minimized.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.